In silver halide color photographic materials, images are formed by reaction of oxidized silver halide developing agent and a dye precursor known as a coupler. In forming such images, it has become relatively common practice in the art to incorporate image-modifying compounds into either the developing solutions or the photographic materials themselves. These image-modifying compounds can impact such photographic properties as sharpness, granularity, contrast and color reproduction.
Incorporation of image-modifying compounds into developing solutions typically limits the ability of the compounds to adequately impact the photographic element since they must diffuse through multiple emulsion, filter or support layers. Direct incorporation of image-modifying compounds into photographic materials, by contrast, often leads to unacceptable image reproduction as such compounds can prematurely interact with other components of the photographic elements, or can decompose during shelf keeping.
It has, thus, become accepted to attach these image-modifying compounds to coupler moieties and to have them released in an imagewise manner during development of the photographic material. This, however, has the dual disadvantage of requiring image formation (as the coupler moiety reacts with oxidized developer) whenever the presence of an image-modifying compound is desired, and of providing only an imagewise release of the image-modifying compound.
There are known alternative means for incorporating image-modifying compounds into photographic materials. Image modifying compounds have been inactivated by blocking, for example, U.S. Pat. Nos. 4,684,604; 4,350,752; 5,019,492; 3,674,478; 5,116,717; and 5,567,577. The present invention offers advantages over these known methods. The compounds described in U.S. Pat. No. 4,684,604 require oxidation with oxidized developer to provide image-wise release of photographic reagents. A scientific study (Getz, et al., J. Org. Chem., 1993, 58, 4913-8) compared the release of phenols from the types of blocking groups employed in U.S. Pat. No. 4,350,752 and one type of the present invention. The cited blocking group of the present invention released phenols faster than the corresponding blocking group of U.S. Pat. No. 4,350,752. Thus, compounds of the present invention can provide faster release. The blocked reagents of U.S. Pat. No. 5,019,492 require a dinucleophile for unblocking. Those of U.S. Pat. No. 3,674,478 are described for release in instant integral elements at high (pH&gt;13). The compounds of U.S. Pat. No. 5,116,717 and U.S. Pat. No. 5,567,577 unblock via nucleophilic aromatic substitution and are, thus, dependent on the concentrations of all nucleophiles in the system (and not alkaline hydrolysis alone).
By contrast, the release compounds of U.S. Pat. No. 5,567,577 can release development inhibitors in a non-imagewise manner, and as a result of exposure to nucleophiles normally present in the processing solutions. These release compounds provide excellent results when incorporated into reversal elements that are push processed. Push processing is a speed adjusting process utilized to compensate for insufficient exposure of the color records of a color reversal light sensitive material. Typically, it is accomplished by "pushing" the first of the development stages (that is, black and white) of reversal processing; that is, it is accomplished by prolonging the period of first development longer than that employed in normal processing. Often, however, push processing results in a degradation of color balance as the increase in speed of one color record does not match that of the other color records.
The release compounds of U.S. Pat. No. 5,567,577 are useful in elements that are push processed because they tend to release their development inhibitors after extended development times. Thus, they impact the characteristics of the photographic element primarily after the initial development phase. This allows one to affect color balance by slowing the development of one silver halide emulsion layer during the push phase while simultaneously allowing the other silver halide emulsion layers to continue developing without restraint.
Although some of the blocked or timed inhibitors known in the art are capable of impacting photographic properties primarily during the push phase of reversal processing, at certain levels or in certain photographic elements, they may be inadequate for completely controlling color balance. For this reason, it is desired to provide a mechanism by which control over color correction during push processing is optimized.